This invention generally relates to the Elmore Model, and more specifically relates to enhancements to the Elmore Model so that wire delays can be more accurately estimated.
The Elmore Model is a mathematical model which is used to estimate the delays at tapping points along a RC line. In other words, it is a tool for estimating the delay associated with providing a signal over a wire to a capacitive load. The Elmore Model is widely used in circuit design. For example, the Elmore Model is widely used during construction of a balanced clock tree (BCT) at different levels of clock net partition. The Elmore Model is described in several publications. For example, see W. C. Elmore, “The transient response of damped linear networks with particular regard to wide-band amplifier”, J Applied Physics, Vol. 19, no. 1, pp. 55-63, January 1948, and J. Vlach, “Numerical method for transient responses of linear networks with lumped, distributed or mixed parameters” Journal of the Franklin Institute, Vol. 288, No. 2, pp. 99-113, August 1969. Generally, one having ordinary skill the art is very familiar with the Elmore Model.
While the Elmore Model is a helpful model to use for wire delay estimations, the Elmore Model is not perfect, and very often introduces some error. In other words, the actual or real delay is often different than the delay as calculated using the Elmore Model. This error may be compounded when attempting to calculate skew using the Elmore Model, where one delay calculation is compared to another. Obviously, if the Elmore Model were to be improved or enhanced, estimations using the Elmore Model would be more accurate. This would improve designs. For example, if the Elmore Model were to be improved or enhanced, clock skew can be minimized among partition groups in a balanced clock tree (BCT).
Additionally, in the prior art, when the Elmore Model is used to estimate the delay associated a clock buffer output, the output resistor of the clock buffer is not considered, and this impacts delay and clock skew estimations.